Method of making alkyl benzenes



Patented Apr. 3, 1934 UNITED STATES METHOD OF MAKING ALKYL BENZENES Joseph G. Davidson; Yonkers, N. Y., assignor to Carbide and Carbon, Chemicals Corporation, a corporation of New York No Drawing. Original application January 26,

1928, Serial No. 245,057. Divided and this application November 8, 1929, Serial No.'405,843

9 Claims. (01. 260-168) The invention relates to improved motor fuels, and specifically to method of making desulphurized alkyl benzene-containing liquids for use in such fuels.

Benzene is extensively used in high-compression fuel blends. Certain of the alkyl benzenes, for example toluene (monomethyl benzene) and the xylenes (dimethyl benzenes) have been tested and found to possess substantial antiknock properties. Large percentages of these substances are required to make acceptable blends for high compression motors. Because of the limited supply of toluene and xylene and the demand for them for other purposes there is no prospect that they will become commercially important as antiknock agents.

I have found that the higher homologues of the methyl benzenes, such as the ethyl and isopropyl benzenes, are effective antiknock agents. These substances have not been used as antiknock fuels to my knowledge, except insofar as they may have been introduced in insignificant proportions into certain blends containing tar oil distillates, it being probable that such distillates contain small quantities of the higher alkyl benzenes. In the blends in question the higher alkyl benzenes if present form so small a proportion of the total antiknock agents that their effect is indeterminate and unimportant.

The ethyl benzenes constitute an important group among the antiknock compounds comprised by my invention. A great number of such compounds are possible in view of the fact that all the hydrogen atoms of the benzene molecule are replaceable by ethyl groups, and the fact that substitutions of ethyl groups and other alkyl groups may occur in the same benzene molecule. Numerous propyl, isopropyl and butyl benzenes are also possible for the same reasons. My researches indicate that any of the ethyl benzenes and their higher homologues which have boiling points within the permissible range for motor fuels are 'useful antiknock agents, and that a mixture of compounds of this group, (which mixture may also contain benzene, toluene or xylenes) has certain advantages over a single compound as an antiknock agent. The boiling points of some of the alkyl benzenes are approximately as follows:

Monoethyl benzene 134 C. Monoisopropyl benzene 151 C. Monopropyl benzene 157 C. Monobutyl benzene 183 C.

The alkyl benzenes containing ethyl or higher alkyl groups are more effective antiknock agents than benzene itself. As is well known it is diflicult to express antiknock properties quantitatively but it may be noted that a fuel containing a standard blending base and 30% by volume of monoethyl benzene can be used at as high compressions as a blend containing the same base and 45% by volume of benzene, and that in other blends monoethyl benzene is likewise about 50% more efieotive than benzene. Alkyl benzenes of higher molecular weight than the monoethyl compound appear to be even more effective.

Antiknock blends now in use contain up to or even more of benzenes. It is obvious that such a proportion oi an antiknock agent which consists largely of. a single chemical compound Will seriously change the boiling curve of the fuel. Since monoethyl benzene is more effective, the proportion used will be less than in the case of benzene, but where a fuel for very high compressions is required, the addition of enough monoethyl benzene to suppress detonation may detrimentally affect the boiling curve of the fuel. I therefore prefer in many cases to add a mixture of ethyl benzenes and higher alkyl benzenes, with or without methyl benzenes and benzene itself, thereby producing a blend which is satisfactory as to both boiling curve and antiknock properties. The complete fuel may of course contain antiknock materials other than aromatic hydrocarbons, and such additional antiknock material may be mixedwith the alkyl benzene material so that it is only necessary to add the blending base to produce the finished blend.

The freezing point of benzene is about 5 C. When very high proportions of benzene are used in a blend, difficulties may be encountered due to solidification at the carburetor jets when the motor using the fuel is exposed to very low temperatures, such as prevail at, high altitudes. Monoethylbenzene has a higher boiling point than benzene yet its freezing point is about 90 C., so that theuse of ethylbenzene as the antiknock agent avoids the diflieulty referred to.

The ethyl and higher alkyl benzenes are not now obtainable in quantity, and I have therefore developed a method for their manufacture.

According to this method the compounds are produced by the treatment of benzene or alkyl benzene with an olefine in'the presence of aluminum chloride or other suitable catalyst. Energetic agitation greatly accelerates the reaction, as does also an elevated temperature approaching the boiling point of the liquid phase in the reaction vessel. Superatmospheric pressures may be used to permit the temperature to be raised still higher but this is unnecessary.

I prefer a countercurrent flow of the olefine and the liquid to be alkylated, the gas being preferably injected in finely divided condition into a descending stream of liquid, but many other arrangements may be used. As aluminum chloride, ferric chloride and the like are readily hydrolized, the reacting materials should be dry or nearly so. It may be assumed that traces of water must be present to produce a little hydrochloric acid to convert the olefine into a chlorhydrocarbon, which then reacts in the manner first studied by Friedel and Crafts, the acid being regenerated. In practicing the process on a commercial scale the traces of moisture assumed to be'necessary will'be present in the raw materials.

If the reacting materials are reasonably dry, the catalyst, for example aluminum chloride, is but little impaired during the process and may be used for a prolonged period. When the liquid is treated in batches the aluminum chloride settles out as a sludge at the end of the alkylation and may be left in the reaction vessel or returned to it, a small quantity of fresh catalyst being added from time to time to balance mechanical and chemical losses. Excellent results have been obtained by alkylating benzene in batches in the presence of 20% of aluminum chloride and returning the catalyst sludge to the next batch together with about 2% of fresh aluminum chloride.

Even when only one olefine is present in the gases with which the benzene is treated, a plurality of compounds are formed. Substituted benzenes containing two ethyl groups or more are formed while substantial quantities of unchanged benzene are still present. Prolonged ethylation is required to transform a high proportion of the benzene, and this tends to give a high content of polyethylbenzenes. If these latter compounds are to be excluded from the product the latter can be fractionated leaving the high-boiling compounds as a still residue. This residue is advantageously added to a subsequent lot of benzene to be alkylated, so that when alkylation proceeds to equilibrium among the various compounds a large proportion of the applied olefine is converted into the desired low-boiling compounds. As a consequence only one lot of the higher compounds is produced regardless of the number of batches of benzene alkylat-ed. If the higher compounds were not returned to the reaction vessel, an additional lot of them would be produced in alkylating each batch.

One of the most striking and valuable results of the process described above is the desulphurization of the benzene during the alkylation.

.Sulphur is a common impurity in commercial benzene and is often present in quantities which are regarded as seriously detrimental in motor fuels. The sulphur appears to be present principally as thiophene and as carbon disulphide. I have found that alkylation carried out in the presence of aluminum chloride or equivalent catalyst removes sulphur practically quantitatively. Thus, in one test benzene containing 0.06% of sulphur gave a product quite free from sulphur. The steps which occur in the desulphurization are not known and are probably complicated. Aluminum chloride has been used for the desulphurization of hydrocarbon materials but under conditions quite different from those which obtain in my process. My experiments indicate that the olefine present plays a part in the desulphurization, possibly converting some of the sulphur compounds into substances which are more reactive with the aluminum chloride or with substances formed in the process.

It is by no means necessary to use a pure olefine in the process. Admixed gases such as hydrogen and the lower parafiine hydrocarbons are not reactive to any detrimental extent with the materials used, and if they are not present in too large proportions they act only as diluents, diminishing the speed of reaction somewhat but being otherwise unobjectionable.

It is also possible, and is often desirable, to use a" mixture of olefines, with or without non-reactive diluents. The product may then contain a series of compounds corresponding to each olefine, and in addition may contain compounds in which different alkyl groups have been substituted in the same molecule. The diversity of possible compounds is thus so great that excessive irregularities in the'boiling curve may be avoided. By varying the proportions of the several olefines used the composition of the product can be more or less closely controlled.

The olefine or mixture of olefines used in the process may be prepared in any usual or suitable way as from alcohols, from gaseous or liquid parafline hydrocarbons by pyrolysis, or from shale, coal and other carbonaceous materials by destructive distillation.

Methyl or other alkyl benzenes may be substituted for or mixed with benzene to produce the material to be alkylated, as ethyl and higher alkyl groups can be introduced ,into the methyl benzenes by the method which has been described. All the compositions included in the invention contain at least one benzene derivative having a substituted alkyl group which contains a plurality of carbon atoms.

Since the alkylation of benzene results in an increased quantity of material, and since the alkylated material is a more effective antiknock than the benzene, it will be apparent that the invention provides a method whereby a greatly increased quantity of high-compression fuel can be prepared from the benzene now available. It is estimated that this increase may be two-fold or greater. The blends made up with the alkyl benzenes, because of their lower sulphur content, smoother boiling curve and other advantages are superior to those now made up from benzene.

I have referred herein to prior high-compression fuels made up with tar-oil distillates, and have also referred to the supposed presence of small quantities of higher alkyl benzenes in these distillates and hence in the blends made from them. The tar-oil distillates which have a boiling range permitting their use in motor fuels are largely composed of methyl benzenes such as toluene, xylenes and mesitylene. The composition of the tar-oil distillates cannot be closely controlled; the distillates may be seriously contaminated with sulphur; the quantity of distillates available is strictly limited; and there is a large demand for the methyl benzenes of which they are largely composed for other purposes. It will be evident that my invention by artificially producing a sulphur-free antiknock from a plentiful raw material avoids the foregoing objections.

This application is a division of my application, Serial No. 245,057, filed January 6, 1928.

I claim:-

1. The method which comprises mixing sulphur-contaminated commercial benzene with an alkylating catalyst of the Friedel-Crafts type;

absorbing an oleflne in the mixture to produce a desulphurized liquid containing alkyl benzene;

. and separating said liquid from the catalyst.

liquid from the catalyst.

3. The method which comprises intimately mixing sulphur-contaminated aromatic hydrocarbons of the benzene series with an olefine and aluminum chloride to produce a desulphurized liquidcontaim'ng alkyl benzene.

4. The methodwhich comprises treating a mixture of sulphur-contaminated benzene and an al-- kylating catalyst of the Friedel-Crafts type with oleflne-containing gas until a product containing several alkyl benzenes is formed; separating a high-boiling alkyl benzene fraction from said product; mixing benzene with said high-boiling alkyl benzene fraction; and treating the mixture with olefine-containing gas in the presence of an alkylating catalyst of the aforesaid type.

5. The method which comprises treating a mixture of sulphur-contaminated benzene and an alkylating catalyst of the group consisting of aluminum chloride and iron chloride with olefinecontaining gas until a product containing several alkyl benzenes is formed; separating a high-boiling alkyl benzene fraction from said product; mixing benzene with the said high boiling alkyl benzene fraction; and treating the mixture with olefine-containing gas in the presence of an alkylating catalyst of the aforesaid group.

6. The method which comprises treating sulphur-contaminated benzene in admixture with about 20% of its weight of an alkylating. catalyst of the group consisting of aluminum chloride and iron chloride with an olefine-containing gas at a temperature approaching the boiling point of the liquid phase of said mixture until a prodnot containing several alkyl benzenes is formed;

separating a high-boiling alkyl benzene fractionand said catalyst from said product; mixing benzene with the said high-boiling alkyl benzene 'fraction containing said catalyst; and treating the mixture .with olefine-containing gas in the presence of about 2% of its weight of additional alkylating catalyst selected from the aforesaid group.

-7. The method which comprises treating a mixture of sulphur-contaminated benzene and an alkylating catalyst consisting of iron chloride with olefine-containing gas until a product containing several alkyl benzenes is formed; separating a high-boiling alkyl benzene fraction from said product; mixing benzene with the said highboiling alkyl benzene fraction; and treating the mixture with olefine-containing gas in the presence of an alkylating catalyst consisting of iron chloride.

8. The method which comprises treating a mixture of sulphur-contaminated benzene with an alkylating catalyst consisting of aluminum chloride with oleflne-containing gas until a product containing several alkyl benzenes is formed; separating a high-boiling alkyl benzene fraction from the product; mixing benzene with the said highboiling alkyl benzene fraction; and treating the mixture with oleflne-containing gas in the presence of an alkylating catalyst consisting of aluminum chloride.

9. The method which comprises treating sulphur-contaminated benzene in admixture with about 20% of its weight of an alkylating catalyst consisting of aluminum chloride with an oleflnecontaining gas at a temperature approaching the boiling point of the liquid phase of said mixture until a product containing several alkyl benzenes is formed; separating a high-boiling alkyl benzene fraction and said catalyst from said product; mixing benzene with the said highboiling alkyl benzene fraction containing said catalyst; and treating the mixture with'clefinecontaining gas in the presence of about 2% of its weight of additional aluminum clfloride.

JOSEPH G. DAVIDSON. 

